Intense Ultraviolet Radiation Research Articles

Growth and Biosynthesis of Phenolic Compounds of Canola (Brassica napus L.) to Different Ultraviolet (UV)-B Wavelengths in a Plant Factory with Artificial Light.

The application of ultraviolet-B (UV-B) irradiation to supplement visible light as an elicitor to increase bioactive compounds under controlled conditions is increasing. This study aimed to evaluate the effects of UV-B dose and wavelength region (280–300 and 300–320 nm) on the morphological, physiological, and biochemical responses of canola plants (Brassica napus L.). Canola plants (17 days after sowing) were subjected to various UV-B intensities (i.e., 0.3, 0.6, and 0.9 W m−2) and were divided into cut and non-cut treatments for each UV treatment. Plant growth parameters exhibited different trends based on the treated UV irradiation intensity. Plant growth gradually decreased as the UV irradiation intensity and exposure time increased. Despite the same UV irradiation intensity, plant response varied significantly depending on the presence or absence of a short-wavelength cut filter (<300 nm). Canola plants suffered more leaf damage in nonfilter treatments containing shorter wavelengths (280–300 nm). UV treatment effectively activates the expression of secondary metabolite biosynthetic genes, differing depending on the UV irradiation intensity. Our results suggest that both UV irradiation intensity and wavelength should be considered when enhancing antioxidant phytochemicals without inhibiting plant growth in a plant factory with artificial light.

Seawater Acidification Exacerbates the Negative Effects of UVR on the Growth of the Bloom-Forming Diatom Skeletonema costatum

Climate changes such as seawater acidification caused by rising atmospheric CO2 and increased ultraviolet radiation (UVR) intensity resulting from shoaling of the upper mixed layer may interact to influence the physiological performance of marine primary producers. But few studies have investigated long-term (&amp;gt;30 days) effects of UVR under seawater acidification conditions, along with less attention on the differential effects of long- and short-wavelength UVA. In the present study, four spectral treatments (&amp;gt;280, &amp;gt;320, &amp;gt;360, and &amp;gt;400 nm) under two pCO2 levels (400 and 1,000 μatm) were set to investigate the interactive effects of seawater acidification and UVR on the bloom-forming diatom Skeletonema costatum. The results showed that UVR decreased growth and effective quantum yield of Photosystem II (PSII) by 9%–16% and 11%–24%, respectively, but it enhanced cell sizes significantly. Long- and short-wavelength UVA showed differential effects on cell volume and the effective quantum yield of PSII, especially at the elevated CO2 level. Generally, seawater acidification depressed the effective quantum yield of PSII and cell volume by 6%–18% and 8%–39%, respectively. Additionally, the contents of key PSII proteins (D1 and D2) decreased at the elevated CO2 level. Elevated CO2 significantly increased the inhibition of UVR on growth in the &amp;gt;280 nm spectral treatment when compared with ambient CO2, while it showed no effects in other spectral treatments. Overall, the results indicate that the effects of seawater acidification on the ubiquitous diatom are light wavelength-dependent.

Optical properties of broadband reflection of cholesteric liquid crystal by thermal diffusion of benzotriazoles.

Polymer stabilized cholesteric liquid crystal broadband reflective films are prepared by the thermal diffusion of a benzotriazoles organic ultraviolet (UV) absorber (UV-327) combined with photopolymerization. A gradient of UV intensity is established in the direction of film thickness, inducing the formation of a pitch gradient distribution, thus broadening the reflected bandwidth. The effects of UV-327 concentration, UV irradiation intensity, irradiation time, polymerization temperature, and C6M concentration on the reflected bandwidth of the sample are examined in detail. The results indicate that the diffusion method of the organic UV absorber enables the reflected bandwidth to be broadened under appropriate conditions.

Aging Behavior of High-Viscosity Modified Asphalt Binder Based on Infrared Spectrum Test.

In the rapid development of sponge city construction in China, porous asphalt pavement has been widely used. The high-viscosity modified asphalt used for porous asphalt pavements is utilised in a complex aging environment. In this study, infrared spectroscopy was used to test the changes in the functional groups of high-viscosity modified asphalt under the influence of ultraviolet radiation intensity, high temperature, and water corrosion conditions. The research results showed that under the influence of several environmental factors, the high-viscosity modified asphalt has no chemical reaction but does undergo physical changes. From the perspective of the functional group index, the carbonyl index is more suitable for evaluating the degree of ultraviolet aging, and the sulfoxide group index is more suitable for evaluating the effect of temperature on aging. The high-viscosity modified asphalt aging kinetic models, established with different functional group indexes as indicators, have different activation energies. The aging kinetic model established with the carbonyl index is more suitable for simulating traditional thermal-oxidative aging. This study provides a better plan to reveal the influence of different environmental factors on the aging performance of high-viscosity modified asphalt under complex environmental conditions.

Modeling of ultraviolet propagation from air to human epidermis with wavelength range of 200–300 nm

Ultraviolet (UV) technology plays an important role in the fields of sterilization, disinfection, and short-range wireless optical communications. In this Letter, a theoretical model to determine the UV radiation intensity (UVRI) on human skin is put forward based on the Monte Carlo method, where the UV wavelength ranges from 200 to 300 nm. Meanwhile, the UVRI evaluation algorithm is provided to reproduce the simulation results. Furthermore, the penetration depth of UV radiation in the human epidermis is investigated, which can be used to assess whether UV radiation causes damage to human health. Simulation results coincide with the existing experimental results that the 222-nm UV radiation is harmless to humans at the given dose of 1.7 mJ/cm2. This work provides theoretical guidelines for the power control of a UV system when humans are in the vicinity.

Variation and adaptation in leaf sulfur content across China

Abstract Sulfur is an essential functional element in leaves, and it plays important roles in regulating plant growth, development and abiotic stress resistance in natural communities. However, there has been limited information on the spatial variation in leaf sulfur content (LSC) and adaptive characters on a large community scale. Sulfur in leaves of 2207 plant species from 80 widespread ecosystems (31 forests, 38 grasslands and 11 deserts) in China was measured. One-way analysis of variance with Duncan’s multiple-range tests were used to evaluate the differences in LSC among different plant growth forms and ecosystems. We fitted the relationships of LSC to spatial and climate factors using regression. Structural equation modeling analysis and phylogenetic analysis helped us further explore the main factors of LSC variation. LSC ranged from 0.15 to 48.64 g kg–1, with an average of 2.13 ± 0.04 g kg–1 at the community scale in China. We observed significant spatial variation in LSC among different ecosystems and taxa. Overall, LSC was higher in arid areas and herbs. Furthermore, higher LSC was observed under environments of drought, low temperatures and intense ultraviolet radiation. Temperature, precipitation, radiation, soil sulfur content and aridity jointly regulated LSC, explaining 79% of the spatial variation. However, LSC was not significantly related to phylogeny. Our results demonstrate that LSC plays an important role in plant adaptations to extreme environments and further extend our understanding of the biological function of sulfur from the organ to the community level. These findings highlight the importance of sulfur metabolism for our understanding of the impact of global climate change on plants.

Superhydrophobic porous polyvinylidene fluoride monolith with outstanding environmental suitability for high-efficient continuous oil/water separation under harsh conditions

The actual cleanup of oil spill and chemical leakage is usually implemented in harsh environments, thus oil absorbents possessing excellent environmental suitability are urgently required for high-efficiency oil/water separation. Herein, a novel three-dimensional porous polyvinylidene fluoride (PVDF) monolith with multi-environmental tolerance was facilely prepared via thermally impacted nonsolvent-induced phase separation method. In view of its unique pore structure and low surface energy, the PVDF monolith owned super-hydrophobicity (water contact angle = 154°) and super-oleophilicity (oil contact angle = 0°) without any modification. As an oil absorbent, the porous monolith exhibited outstanding oil/water separation performance for various oils/organic solvents, such as preeminent separation efficiency, high saturation absorption capacity (21.3 g g−1) and rapid absorption speed (reaching saturation state within 15 s). More importantly, the monolith revealed stable and prominent oil/water separation capability under harsh conditions involving intense ultraviolet radiation (72 h), rapidly alternating temperature (−20 to 65 °C), extreme pH, oil-water emulsion, strongly turbulent water, suspended solids (sand and tea leaf). It is worth noting that the monolith was capable of continuously and efficiently separating oil/organic solvent from water by a simple pump-assisted system (soybean oil flux reached 3520 L m−2 h−1 at 0.06 MPa). A small piece of PVDF monolith (0.132 g) was able to continuously separate at least 16,000 times its own weight of soybean oil and could be reused for 5 cycles. Based on the superior environmental suitability and continuous oil/water separation capability, the porous PVDF monolith has a tremendous potential to clean up large-scale oil contaminants in leakage accidents.

The effect of ultraviolet radiation on the incidence and severity of major mental illness using birth month, birth year, and sunspot data

Background and objectivesThe evaluation of the severity of patients afflicted with major mental illness (MMI) has been problematic because of confounding variables and genetic variability. There have been multiple studies that suggest several human diseases, especially schizophrenia, are predisposed to be born in certain months or seasons. This observation implied an epigenetic effect of sunlight, likely ultraviolet radiation (UVR), which is damaging to DNA, especially in an embryo. This paper outlines a method to evaluate the severity of schizophrenia (SZ), bipolar disorder (BPD), and schizoaffective disorder (SZ-AFF) using the month/year of birth of those affected compared to the month/year of birth of the general population (GP). RelevanceOur previous research found that more intense UVR (equal to or greater than 90 sunspot number (SSN)) had a negative effect on the average human lifespan. Also, human birth rates vary in frequency by month of birth reflecting variables like availability of food, sunlight, and other unknown epigenetic factors. We wanted to see if the patient month of birth varied from the average birth months of the general population and if UVR has an epigenetic effect promoting these diseases. MethodsWe obtained the month and year of birth of 1,233 patients admitted over a 15-year period to Maine's largest state psychiatric hospital and counted the months of birth for each diagnosis of SZ, BPD, and SZ-AFF, and compared these results to the general population's birth months of 4,265,555 persons from U. S. Census Year 2006. The number of patients in each month was normalized to August and compared with the normalized birth months of the general population (GP). Plots of the normalized months were considered rates of change (e.g., derivatives) and their respective integrals gave domains of each mental illness relative to the GP. Normalizing the GP to unity was then related to the factor 1.28, e.g., 28% more entropy, deduced from the Sun's fractal dimension imprinted on biological organisms. ResultsThe percent of patients meeting our criterion for severity: SZ = 27%; BPD = 26%; SZ-AFF = 100%. ConclusionsHigh UVR intensity or a rapid increase in UVR in early gestation are likely epigenetic triggers of major mental illness. BPD is more epigenetically affected than SZ or SZ-AFF disorders. We found that 52% of 1,233 patients comprised the core function of a tertiary-care psychiatric hospital. Also, mental illness exacerbated when the median SSN doubled. This work also validates the Kraeplinian dichotomy. What is new in this researchThis paper offers a new paradigm for evaluating the severity of MMI and supports significant epigenetic effects from UVR.

Generalizations of the R-Matrix Method to the Treatment of the Interaction of Short-Pulse Electromagnetic Radiation with Atoms

Since its initial development in the 1970s by Phil Burke and his collaborators, the R-matrix theory and associated computer codes have become the method of choice for the calculation of accurate data for general electron–atom/ion/molecule collision and photoionization processes. The use of a non-orthogonal set of orbitals based on B-splines, now called the B-spline R-matrix (BSR) approach, was pioneered by Zatsarinny. It has considerably extended the flexibility of the approach and improved particularly the treatment of complex many-electron atomic and ionic targets, for which accurate data are needed in many modelling applications for processes involving low-temperature plasmas. Both the original R-matrix approach and the BSR method have been extended to the interaction of short, intense electromagnetic (EM) radiation with atoms and molecules. Here, we provide an overview of the theoretical tools that were required to facilitate the extension of the theory to the time domain. As an example of a practical application, we show results for two-photon ionization of argon by intense short-pulse extreme ultraviolet radiation.

Time-resolved measurement of radical populations in extreme-ultraviolet-light-induced hydrogen plasma

We have investigated hydrogen plasma induced by intense extreme ultraviolet (EUV) radiation by measuring the plasma parameters and population density of radicals, which is expected to clean the tin contamination on the optics in EUV sources, using a time-resolved optical emission spectroscopy. The obtained electron density was n e = (2 ± 0.4) × 1013 cm−3, and the electron temperature was T e = 1 ± 0.2 eV. The electron density was five orders of magnitude higher than that of previous study. The radical population density determined by the experiment was consistent with that calculated with a collisional radiative model, showing excitation and recombination are dominant production processes.

The Role of the Global Solar UV Index for Sun Protection of Children in German Kindergartens.

More than twenty-five years ago, the Global Solar UV index (UVI) was introduced as a simple means of visualizing the intensity of ultraviolet radiation and to alert people to the need for sun protection. In our survey, among directors of 436 kindergartens in southern Germany we investigated the level of awareness and knowledge about the UVI as well as the practical consequences for sun protection in kindergartens. Less than half of the directors (n = 208, 47.7%) had ever heard of the UVI, and only a small minority of them (n = 34, 8.7%) used the daily UVI information to adapt sun protective measures in their kindergartens. Detailed knowledge about the UVI was a rarity among the respondents. The proportion of respondents with self-perceived detailed UVI knowledge was five times higher than the actual knowledge assessed by an in-depth structured interview using open-ended questions about the UVI (14.2% vs. 2.8%). No clear relationship between UVI awareness, knowledge, and use and directors’ age and gender was found. The UVI-related variables also showed no association with directors’ knowledge of risk factors for skin cancer and their attitudes towards tanned skin. Overall, the results paint a sobering picture regarding the penetration of the UVI into sun protection policies of German kindergartens. Future public health campaigns should aim to increase the awareness and understanding of the UVI as well as its relevance for sun protection of children.

A Simple Preparation Method of Graphene and TiO2 Loaded Activated Carbon Fiber and Its Application for Indoor Formaldehyde Degradation

Formaldehyde has a significant impact on human health. This study used a simple dipping method to load graphene-titanium dioxide (GR-TiO2) on activated carbon fibers (ACFs). The microstructure of GR-TiO2/ACF hybrid material was observed by SEM, combined with XRD and BET analysis. The result showed that the GR-TiO2/ACF hybrid material had a specific surface area of 893.08 m2/g and average pore size of 2.35 nm. The formaldehyde degradation efficiency of the prepared material was tested under different conditions, such as ultraviolet (UV) radiation, air supply volume, relative humidity, initial mass concentration. The results showed that the UV radiation intensity, airflow and the initial mass concentration were positively correlated with the formaldehyde removal rate, and the relative humidity was negatively correlated with the formaldehyde removal rate. The GR-TiO2/ACF hybrid material had a maximum formaldehyde removal rate of 85.54% within 120 min.

Influence of Different Ultraviolet Radiation Intensities on the Corrosion Behavior of Type 316 Stainless Steel in a Simulated Salt-Lake Atmospheric Environment

Influence of Different Ultraviolet Radiation Intensities on the Corrosion Behavior of Type 316 Stainless Steel in a Simulated Salt-Lake Atmospheric Environment

Effect of UV Radiation on Structural Damage and Tribological Properties of Mo/MoS2-Pb-PbS Composite Films

To investigate ultraviolet (UV) radiation effects on tribological properties of Mo/MoS2-Pb-PbS film, ultraviolet (UV) radiation exposure tests were carried out for 20 h, 40 h, 60 h and 80 h by space UV radiation simulation device developed by our team, which can reach 3 UV radiation intensity. The exposure time in test was equivalent to the radiation of 100 h, 200 h, 300 h and 400 h in the space. Then, the vacuum friction test of Mo/MoS2-Pb-PbS thin film was performed under the 6 N load and 100 r/min, and friction test time of each sample was 20 min. By SEM, TEM, XPS the composition and morphology of Mo/MoS2-Pb-PbS film surface after UV radiation were analyzed. UV radiation could change the microstructure significantly and relative content of S element and MoS2 on the surface of the films decreased, and light mass loss of the films occurred. The tribological properties will also recover with the increase of sliding time, although the friction coefficient fluctuation of the film increased at the starting stage of the friction test. The damage of Mo/MoS2-Pb-PbS under UV irradiation was mainly caused by the volatilization of the enriched S element in the surface layer due to the high temperature heating of UV irradiation.

Photobiology of the keystone genus Metarhizium.

Metarhizium fungi are soil-inhabiting ascomycetes which are saprotrophs, symbionts of plants, pathogens of insects, and participate in other trophic/ecological interactions, thereby performing multiple essential ecosystem services. Metarhizium species are used to control insect pests of crop plants and insects that act as vectors of human and animal diseases. To fulfil their functions in the environment and as biocontrol agents, these fungi must endure cellular stresses imposed by the environment, one of the most potent of which is solar ultraviolet (UV) radiation. Here, we examine the cellular stress biology of Metarhizium species in context of their photobiology, showing how photobiology facilitates key aspects of their ecology as keystone microbes and as mycoinsectides. The biophysical basis of UV-induced damage to Metarhizium, and mechanistic basis of molecular and cellular responses to effect damage repair, are discussed and interpreted in relation to the solar radiation received on Earth. We analyse the interplay between UV and visible light and how the latter increases cellular tolerance to the former via expression of a photolyase gene. By integrating current knowledge, we propose the mechanism through which Metarhizium species use the visible fraction of (low-UV) early-morning light to mitigate potentially lethal damage from intense UV radiation later in the day. We also show how this mechanism could increase Metarhizium environmental persistence and improve its bioinsecticide performance. We discuss the finding that visible light modulates stress biology in the context of further work needed on Metarhizium ecology in natural and agricultural ecosystems, and as keystone microbes that provide essential services within Earth's biosphere.

Exploring the Distribution of Ultraviolet Radiation Intensity of Parabolic Reflector at Different Overall Heights

The global pandemic of coronavirus disease 2019 (COVID-19) has posed a serious threat to human society on both perspectives of health and economy. Ultraviolet (UV) has been verified capable to damage the DNA and RNA of various microorganisms, including the new coronavirus. The parabolic reflector, a key component of the upper-room ultraviolet germicidal irradiation (UVGI) device, plays a vital role in collating and restraining ultraviolet light. In order to deeply understand the influence of the reflector in the device on the spatial distribution and numerical value of the ultraviolet radiation intensity, we measured and simulated the efficacy of the reflector equipped with a single-tube UV lamp. At a distance of 50cm from the reflector, a virtual plane with a side length of 40cm×40cm parallel to the exit port was introduced. At room temperature of 20 °C, measured and simulated reflectors were carried out at three heights A, B, and C, which were 25 cm, 20 cm, and 15 cm. We have concluded that as the height of the reflector increases, the irradiance value in the space also increases; then decreasing the height of the reflector is more conducive to the uniform distribution of the irradiance in the space. In conclusion, exploring the appropriate reflector height to obtain the balance of UV intensity and distribution is meaningful for improving the efficiency of the upper layer device

ЗНЕЗАРАЖЕННЯ ПИТНОЇ ВОДИ ЗА ДОПОМОГОЮ ПЛАЗМИ ЕЛЕКТРИЧНОГО РОЗРЯДУ

For today, taking into account the low efficiency of the disinfection technologies using chlorine-containing compounds and the growing number of chlorine-resistant microorganisms, the question of introducing alternative methods of disinfection in the field of water supply and drainage is relevant. One such alternative method is the treatment of liquids with plasma of electric discharge. This article describes our experiments on the treatment of different types of water from surface sources in Kyiv and water intentionally infected with Escherichia coli (E. coli). The experiments were performed on a laboratory installation with a circulating pump and an ejector-type reactor with integrated electrodes. In the reactor a water-air mixture is formed, in which an electric discharge takes place. The disinfection reactor and at the same time the device for the formation of a heterogeneous water-air environment is an ejector with electrodes inserted into it, which receive pulses of electric current. Discharges initiate a range of different physicochemical phenomena, such as a strong electric field, intense ultraviolet radiation, shock waves of excess pressure and, in particular, the formation of various highly active chemicals such as radicals (OH •, H •, O •) and molecules ( H2O2, H2, O2, O3). All these physicochemical processes occur during the discharge itself, for example, the formation and action of short-lived radicals, as well as the action of relatively long-lived oxidants. The effect of the concentration of microorganisms on the rate and completeness of water disinfection was studied in technical (tap) water with the introduction into the reaction tank of the washoff from two test tubes. This provided an initial concentration of E. coli of 3.4 ∙ 106 CFU / cm3. Water treatment for 30 seconds reduced the concentration of microorganisms by two orders of magnitude (up to 5.4 ∙ 104). After 1 minute of treatment, this figure decreased to 1.7 ∙ 102, and after 3 minutes to 5.2 CFU / cm3, i.e., the treated water corresponded to norms for almost pure water. Experiments have proven the effectiveness of plasma disinfection, even for liquids with a concentration of microorganisms significantly exceeding the maximum allowable concentrations. The content of microorganisms before and after treatment was determined by the method of limiting dilution of samples with subsequent sowing on a nutrient medium in Petri dishes

Intensification of nitrification processes in soil by ultraviolet (UV) irradiation

This study highlights the application of UV radiation for soil treatment with regard to agricultural plant growth intensification. The influence of the parameters of ultraviolet radiation (intensity and wavelength) on the value of the redox potential in the soil was quantified. The experimental tests carried out in soils, plants, seeds with ultraviolet radiation lamps for changing the accumulation of the most mobile nitrate forms of nitrogen were defined.

A DNN-Based UVI Calculation Method Using Representative Color Information of Sun Object Images.

As outdoor activities are necessary for maintaining our health, research interest in environmental conditions such as the weather, atmosphere, and ultraviolet (UV) radiation is increasing. In particular, UV radiation, which can benefit or harm the human body depending on the degree of exposure, is recognized as an essential environmental factor that needs to be identified. However, unlike the weather and atmospheric conditions, which can be identified to some extent by the naked eye, UV radiation corresponds to wavelength bands that humans cannot recognize; hence, the intensity of UV radiation cannot be measured. Recently, although devices and sensors that can measure UV radiation have been launched, it is very difficult for ordinary users to acquire ambient UV radiation information directly because of the cost and inconvenience caused by operating separate devices. Herein, a deep neural network (DNN)-based ultraviolet index (UVI) calculation method is proposed using representative color information of sun object images. First, Mask-region-based convolutional neural networks (R-CNN) are applied to sky images to extract sun object regions and then detect the representative color of the sun object regions. Then, a deep learning model is constructed to calculate the UVI by inputting RGB color values, which are representative colors detected later along with the altitude angle and azimuth of the sun at that time. After selecting each day of spring and autumn, the performance of the proposed method was tested, and it was confirmed that accurate UVI could be calculated within a range of mean absolute error of 0.3.

Distributed electric current and its relation to ultraviolet radiation of the active region

We utilized full magnetic field vector magnetogramsacquired by the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) to calculate vertical electric currents in the NOAA active region (AR) 12192. The AR was tracked between October 22, 2014 and October 25, 2014 with 720 s cadence. We revealed the presence of a large-scale electric current structure – distributed electric current – with the absolute magnitude varying in the range of (40–90)·1012 A. The distributed electric current is supposed to exist throughout the entire AR, and, extending to the upper layers of the solar atmosphere in one part of the AR, it closes through the chromosphere and corona in the remaining part of the AR. To test this assumption, we have compared the temporal variation of the distributed electric current value with the flare activity level (using GOES-15 data), as well as with intensity of ultraviolet radiation (UV) in the AR (using the Atmospheric Imaging Assembly (AIA/SDO) data in channels 94 Å, 193 Å, 304 Å, and 1600 Å). We found that: i) Time intervals of enhanced flare activity are co-temporal with intervals of increased values of the distributed electric current. The absence of rapid changes in the value of the distributed electric current during solar flares can be explained by high inductance of the current-carrying magnetic loops. ii) Rough estimates of the magnetic energy carried by the distributed electric current into the corona yield the values of about 1033–1034 erg for 12192. Onlya small amount of this energy is released during flare processes in the AR. Most of this energy seems to be consumed during other dissipative processes in the corona. iii) Comparison of the temporal variations of intensity in the 193 Å UV-radiation channel with dynamics of the distributed electric current in the AR reveals a good positive correlation between these values (Pearson’s R = 0.63). The absence of a correlation between the distributed electric current value and the intensity of UV radiation in channels 1600 Å, 304 Å and 94 Å might be explained by a low efficiency of the coronal loop heating by ohmic dissipation of electric currents in the corona due to the strong dependence of plasma conductivity on temperature. iv) Our results may support the concept of equivalent LRC circuit of a current-carrying coronal magnetic loop proposed by Alfven and Carlqvist in 1967 and developed by V.V. Zaitsev, A.V. Stepanov, and others. According to this model, the large-scale electric currents must exist in the upper layers of the solar atmosphere and take part in the coronal plasma heating.